1. Field of the Invention
The present invention relates to a synthesized inorganic ion exchange material and a detergent composition containing the same, and more specifically to a synthesized inorganic ion exchange material excellent in ion exchange capacity and alkaline capacity, and having anti-solubility in water, and a detergent composition containing such a synthesized inorganic ion exchange material.
2. Discussion of the Related Art
To date, a large number of chelating agents, ion exchange materials, precipitants, dispersants and other substances have been reported to be used for detergent builders. In recent years, the use of tripolyphosphates has decreased, since they can cause eutrophication in closed freshwater areas such as lakes and marshes. Instead, crystalline aluminosilicates, typically those disclosed in Japanese Patent Laid-Open Nos. 50-12381 and 51-12805, have been commonly used.
Although sodium silicate has an ion exchange capacity not less than that of zeolite, its use has been limited since it is soluble in water. As a means for solving this problem, a method in which sodium silicate is thermally dehydrated, baked and powdered is disclosed in Japanese Patent Laid-Open No. 60-239320, and a method in which part of the silicon of sodium silicate is isomorphously replaced with aluminum in a similar manner is disclosed in Japanese Patent Laid-Open No. 3-93649. However, both methods have problems in that the obtained anti-solubility is insufficient and the ion exchange capacity is low. Also, crystalline calcium silicate alkali hydrates obtained by hydrothermal synthesis are disclosed in Japanese Patent Examined Publication No. 61-59245, but they are substantially unsuitable as detergent builders because of their low ion exchange capacity, though they have sufficient anti-solubility in water. Moreover, because their grain shape is in the form of coarse long fiber or mica, their aqueous dispersibility is low so that the actual ion exchange capacity shows further reduction. Also, DD-279234A1 publication discloses a crystalline magnesium-containing silicate obtained by hydrothermal synthesis, but there is a problem in that this silicate is extremely low in ion exchange capacity, making it impossible to be practically used as a detergent builder.
Crystalline silicates can be structurally classified by their anion form (Friedrich Liebau, "Structural Chemistry of Silicates," p. 72, Springer-Verlag published in 1985). For example, the 4A type zeolite, which is a representative inorganic builder having the structural formula Na.sub.2 O.Al.sub.2 O.sub.3.2SiO.sub.2, is classified as a tectosilicate structure, wherein Si is partially isomorphously replaced with Al. Dimetasilicate (layered silicate), having the structural formula Na.sub.2 O.2SiO.sub.2, is classified as a phyllosilicate structure. Also, the metasilicate having the structural formula CaO.MgO.2SiO.sub.2.nH.sub.2 O (diopside) and the metasilicate such as sodium metasilicate having the structural formula Na.sub.2 O.SiO.sub.2 are classified as an inosilicate (polysilicate) structure.
In more detail, crystalline silicates can be classified by the number of Si-crosslinking oxygen atoms (Si--O--Si). Si-crosslinking oxygen numbers of 4, 3, 2, 1 and 0 are assigned to the Q.sub.4, Q.sub.3, Q.sub.2, Q.sub.1 and Q.sub.0 units, respectively (Y. Tsunawaki, N. Iwamoto, T. Hattori and A. Mitsuishi, "J. Non-Cryst. Solids," vol. 44, p. 369, 1981). With an Si-crosslinking oxygen number of 4, the tectosilicate structure is formed from the Q.sub.4 unit alone. With an Si-crosslinking oxygen number of 3, the phyllosilicate structure is formed from the Q.sub.3 unit alone. With an Si-crosslinking oxygen number of 2.0 to 2.5, the inosilicate structure is formed from the Q.sub.2 unit alone or from the Q.sub.2 and Q.sub.3 units. Specifically, the silicates formed from at least the Q.sub.2 unit such as those defined by the Q.sub.2 unit alone and those defined by both Q.sub.2 unit and Q.sub.3 unit are said to have a chain structure. By contrast, the silicates consisting of the Q.sub.3 unit alone are said to have a layered structure. Therefore, these silicates are clearly distinguishable from each other in view of their structures.
As viewed as inorganic builders for detergents, the above-mentioned silicate compounds can be described as follows: Having the tectosilicate structure formed from the Q.sub.4 unit alone, the 4A type zeolite is so low in aqueous dispersibility that its amount in a detergent is limited, though it possesses a high cationic exchange capacity. Layered silicates having the phyllosilicate structure formed from the Q.sub.3 unit alone, methods for whose preparation are disclosed in Japanese Patent Laid-Open Nos. 60-239320 and 3-93649 as described above, are excellent in aqueous dispersibility because of their hydration property, but they are undesirably highly soluble in water and their cationic exchange capacity is lower than that of the 4A type zeolite. Therefore, these types of silicates do not serve well as builders for detergents.
On the other hand, with the inosilicate structure formed from the Q.sub.2 unit alone or from the Q.sub.2 and Q.sub.3 units, diopside exhibits almost no cationic exchange capacity so that it does not serve well as an inorganic builder. Also, there is another type of inosilicate (Na.sub.2 O.SiO.sub.2), which has a theoretically high cationic exchange capacity, in the form of a crystalline metasilicate, but its water solubility is extremely high so that its structure is destroyed, which results in an extreme decrease in actual cationic exchange capacity. It is, therefore, unsuitable as an inorganic builder.
As described above, it has been difficult to obtain an inorganic ion exchange material which is excellent in both anti-solubility in water and ion exchange capacity, and the development of such an inorganic ion exchange material having improvements in these properties has been in demand.